Someone recommended me a treatment called "Cognitive Behaviour Therapy for Insomnia" - or CBT-I, and it was just amazing. What worked out the most was Sleep Privation and not worrying about my sleep, I Highly recommend this to everyone who is struggling. (Note aside, the first days of sleep privation are an absolute hell, I wanted to literally die, but it's worth at the end).
If you spend 8h total, you can dial back to 7, or as low as 6, on a temporary basis. Once your sleep restructures itself (which doesn't actually take that long), you can increase your total time in bed back to 8.
Even sleep therapy apps are pretty useless as they just regurgitate what ought to be freely available information.
Onset insomnia is (or was) my main thing. I tried this and remember feeling totally dead. Couldn't get through it.
Keeping a steady waking time is the main thing. Rather than limiting myself to 6 or 7 hours I'll stay up reading to a low warm light until sufficient sleep pressure has built up (easy enough to identify). A preceding relaxation routine helps, and time away from electronics. I do a quick yoga stretching thing. If it so happens I hit the sack and can't fall asleep, I'll sit up for a couple of minutes, then try again.